The objective of the proposed research is to define in molecular terms the interaction between the vitamin K-dependent blood coagulation factors (in this context, II, VII, IX, and X), calcium ions, and phospholipid. A model system consisting of bovine prothrombin fragment 1 (residues 1-156) will be employed. Correlations will be sought between fragment 1 structure and its functional properties, namely metal ion binding and metal ion-dependent phospholipid binding. We plan to explore the importance of a variety of structural features of fragment-1 as reflected by a variety of physical properties such as optical spectroscopy, potentiometry, and fluorescene spectroscopy. Metal ion NMR will also be employed.